1. Field of the Invention
The invention relates to a process for the preparation of hardenable binding agents based on cement with the addition of emulsions of bituminous products and, if desired, synthetic materials. These binders may be used for the production of roadway surfaces as well as flexible bases for supporting asphalt or concrete roadway surfaces and for the manufacture of floor finishes as well as of cast objects in the form of pipes, blocks or panels.
2. Description of the Prior Art
As used herein, bituminous products are understood to refer particularly to bitumens, tars, pitch and resins, such as, those obtained for mineral oil and coal by known procedures through distillation or extraction. Bitumens, however, are preferred. Bitumens with a penetration number of 10 to 300 are especially preferred.
It is well known that roadway surfaces may be prepared from bituminous raw materials which have been mixed with mineral fillers, such as, fine gravel, for example. Such roadway surfaces have viscoelastic properties. Under high loads and particularly at elevated temperatures, they tend to permanently deform.
It is also well known that roadway surfaces based on cement concrete may be prepared. These roadway surfaces are distinguished by their hardness and by their load carrying capacity. The inelastic, rigid behavior of these cement-based surfaces is, however, a disadvantage because of the difficulty of repairing such roadway surfaces in the case of damage.
There have been numerous attempts to combine the viscoelastic properties of bitumen/asphalt concrete and asphalt roadway surfaces with the good mechanical properties of roadway surfaces based on cement concrete by adding to the cement, before it sets, aqueous emulsions of bituminous products to which dispersions of synthetic materials may also be added. The bituminous products, referred to in the following as bitumen, are intended to envelope the cement particles completely or partially and, in so doing, totally or partially prevent the formation of bonds between the mineral particles as the cement sets. Admittedly, cement-based products are obtained, whose elastic behavior may be influenced by the nature, quantity and distribution of the bitumen introduced, so that the mechanical properties may be adjusted at will from the rigid to the elastic state.
In German Offenlegungsschrift No. 26 13 075, a rapidly setting mixture is described which is characterized by the fact that it contains an extremely rapidly setting cement with a content of 11CaO.7Al.sub.2 O.sub.3.CaX.sub.2, in which X is a halogen atom, 3CaO.SiO.sub.2 and CaSO.sub.4 as essential components, at least one short-range strength accelerator from the group of calcium aluminates, limes, amines and ethylene glycols, as well as calcium sulfate hemihydrate, at least one emulsion from the group of bituminous emulsions, rubber latexes and resin emulsions and 12 to 50 weight percent of water, based on the total mixture. The bitumen emulsion is characterized by the type of emulsifier used therein and may be a cationic, anionic or nonionic emulsion or an emulsion of the clay type and should contain, for each part by weight of cement, 0.02 to 3 parts by weight and, preferably, 0.15 to 1.5 parts by weight of the emulsion, the parts by weight referring to the nonvolatile components. The bituminous emulsions generally contain 40 to 70 weight percent of bituminous material. The penetration number of the residue obtained from concentrating the bituminous emulsion by evaporation generally is from 10 to 300 at 25.degree. C.
Incompatibility in the mixture is frequently observed on the addition of its aqueous suspension. An aqueous suspension of cement is highly alkaline and has a high cation content. When using an emulsion which has been prepared with an anionic emulsifier, this may lead to precipitation of the emulsifier and to an uncontrolled breaking of the bitumen emulsion. This, in turn, causes an uncontrolled deposition of bitumen particles in the hardened cement and prevents the desired total or partial envelopment of the individual cement particles by bitumen.
On the other hand, emulsions prepared with cationic emulsifiers, whose preferred stability range lies in the acid pH region, break because of the change in the pH value on addition of the cement suspension. With nonionic emulsifiers and with anionic emulsifiers based on sulfates or sulfonates, it is possible to prepare bitumen emulsions which have the advantage of a certain insensitivity to changes in the pH and towards the alkaline earth ions of the cement. However, it is not possible to control the rate of breaking of such emulsions. On mixing with minerals, they undergo heavy foaming and the unbroken emulsion is leached out when a finished coating is exposed to rain before it has fully dried out and set.
Moreover, it is well-known that emulsions containing ionic emulsifiers can be stabilized towards cement by the addition of water soluble colloids, such as, protein degradation products or cellulose ethers or by mixing with swellable minerals, such as, bentonite. The bituminous binding agents may also be emulsified directly in aqueous suspensions of such products. Admittedly, emulsions so prepared are compatible with cement. However, coatings and molded articles prepared with such emulsions tend to form shrinkage cracks on setting as a result of the drying out of the swellable substances contained in these emulsions.